FIG. 2.

Azithromycin affects transcription of quorum-sensing genes. The expression of the transcriptional activator and the autoinducer synthase genes was measured by β-Gal determinations in strain PAO1 cultures grown for 10 h in the absence (azithromycin −) or presence (azithromycin +) of 2 μg of azithromycin/ml, using plasmids pPCS1001(lasR′-lacZ) and pPCS1002(rhR′-lacZ) (A) and plasmids pPCS223(lasI′-lacZ) and pLPRI(rhlI′-lacZ) (B). Exogenous autoinducers were added to the cell culture as indicated (autoinducers +). Results are the mean ± SD of three independent experiments performed in duplicate.